1. Field of the Invention
The present invention relates to a semiconductor device in which a semiconductor chip is mounted via protruding electrodes on conductor wirings of a tape carrier substrate used for a Bump On Film (BOF) or the like, and a method for producing the same.
2. Description of Related Art
In a package such as a BOF (Bump On Film) used for a liquid crystal driver, a tape-shaped base formed of polyimide or the like is used as a wiring board on which a semiconductor chip is to be mounted. FIG. 9 is a sectional view showing a part of an exemplary BOF. The BOF has a structure in which a semiconductor chip 22 is mounted on a flexible tape carrier substrate 21 and protected with a sealing resin 23, and is used mainly as a driver for driving a flat panel display. The tape carrier substrate 21 mainly includes a flexible insulating film base 24, conductor wirings 25 formed on the surface of the film base 24 and bumps 26 formed on the conductor wirings 25. A metal plating film and a layer of solder resist, which is an insulating resin, are formed on the conductor wirings 25 as needed. The bumps 26 are disposed at positions corresponding to electrodes 27 of the semiconductor chip 22, and the conductor wirings 25 on the tape carrier substrate 21 and the electrodes 27 on the semiconductor chip 22 are connected via the bumps 26.
In general, polyimide is used for the film base 24, and copper is used for the conductor wirings 25. The bumps 26 are formed on the conductor wirings 25 in advance. The structure of the tape carrier substrate 21 is shown in FIG. 10, which is a perspective view showing a part of the tape carrier substrate 21. As shown in FIG. 10, a plurality of the conductor wirings 25 are aligned on the film base 24, and the bumps 26 are formed on the conductor wirings 25, respectively. The bumps 26 extend laterally across the conductor wiring 25 and extend to regions on both sides of the conductor wiring 25.
In order to form the bumps 26 on the conductor wirings 25 of the tape carrier substrate 21, a method described in JP 2004-327936 A is used, for example. The processes of this method for producing a tape carrier substrate will be described, with reference to FIG. 11.
FIGS. 11(a1) to 11(f1) are plan views showing a part of a film base in a production process in a conventional example. FIGS. 11(a2) to 11(f2) are sectional views corresponding to FIGS. 11(a1) to 11(f1), respectively. Each of these sectional views is taken along a line A-A′ in FIG. 11(a1). This production process is an exemplary case of forming protruding electrodes by metal plating.
First, as shown in FIG. 11(a1), a film base 24 with a surface on which a plurality of conductor wirings 25 are aligned is prepared. As shown in FIG. 11(b1), a photoresist 28 is formed on-the entire surface of this film base 24. Next, as shown in FIG. 11(c1), an exposure mask 29 for forming bumps is opposed to an upper part of the photoresist 28 formed on the film base 24. A light-transmitting region 29a of the exposure mask 29 has an elongated opening shape that continues so as to cross the plurality of conductor wirings 25 along the alignment direction of the plurality of conductor wirings 25. By light exposure through the light-transmitting region 29a of the exposure mask 29 followed by development, as shown in FIG. 11(d1), an opening of an elongated pattern 28a crossing the conductor wirings 25 is formed in the photoresist 28. This exposes a part of the conductor wirings 25 in the elongated pattern 28a. Subsequently, the exposed part of the conductor wirings 25 is plated with metal through the elongated pattern 28a of the photoresist 28, whereby bumps 26 are formed as shown in FIG. 11(e1). Thereafter, the photoresist 28 is removed, thus obtaining a tape carrier substrate 21 in which the bumps 26 are formed on the conductor wirings 25 as shown in FIG. 11(f1).
As described above, by plating the exposed part of the conductor wirings 25 with the metal through the elongated pattern 28a formed in the photoresist 28, the bumps 26 with the shape illustrated in FIG. 10 can be formed easily. This is because, in the process shown in FIG. 11(e1), not only the upper surface of the conductor wiring 25 but also side surfaces thereof are exposed, and the entire exposed surfaces of the conductor wiring 25 are plated.
In the case where the bumps 26 are formed of copper, the metal plating can be, for example, electroplating at 0.3 to 5 A/dm2 using copper sulfate as a plating solution.
When mounting a semiconductor chip 22 on the tape carrier substrate 21 on which the plurality of conductor wirings 25 are aligned as described above, the bonding process as shown in FIG. 12 is carried out. First, as shown in FIG. 12A, the semiconductor chip 22 and the tape carrier substrate 21 are opposed to each other. At this time, a sealing resin 23 is applied onto the tape carrier substrate 21 in advance, and then the positioning between electrodes 27 and the bumps 26 is conducted. Next, the bonding process as shown in FIG. 12B is carried out for the semiconductor chip 22 and the tape carrier substrate 21 that have been subjected to the positioning. In other words, a bonding tool (not shown) is made to contact the back surface of the semiconductor chip 22 so as to apply a load and ultrasonic vibrations, thereby bonding the electrodes 27 and the bumps 26.
However, in such a bonding technique, the ultrasonic vibrations are applied to the semiconductor chip 22, so that damage such as cracking occurs below the electrodes 27 of the semiconductor chip 22.